Solar cell

ABSTRACT

A solar cell can include a substrate of a first conductive type; an emitter region of a second conductive type opposite the first conductive type and which forms a p-n junction along with the substrate; an anti-reflection layer positioned on the emitter region; a front electrode part electrically connected to the emitter region; and a back electrode part electrically connected to the substrate, wherein the substrate including a first area formed of single crystal silicon and a second area formed of polycrystalline silicon, wherein a thickness of the anti-reflection layer positioned on the first area is less than a thickness of the anti-reflection layer positioned on the second area, wherein a roughness of an incident surface of the substrate in the first area is different from a roughness of the incident surface of the substrate in the second area, and wherein the emitter region is entirely formed on the incident surface of the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/546,940filed on Jul. 11, 2012, which claims priority to and the benefit ofKorean Patent Application No. 10-2011-0075680 filed in the KoreanIntellectual Property Office on Jul. 29, 2011. The entire contents ofthese applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention relate to a solar cell.

2. Description of the Related Art

Recently, as existing energy sources such as petroleum and coal areexpected to be depleted, interests in alternative energy sources forreplacing the existing energy sources are increasing. Among thealternative energy sources, solar cells for generating electric energyfrom solar energy have been particularly spotlighted.

A solar cell generally includes semiconductor parts, which respectivelyhave different conductive types, for example, a p-type and an n-type andthus form a p-n junction, and electrodes respectively connected to thesemiconductor parts of the different conductive types.

When light is incident on the solar cell, carriers including electronsand holes are produced in the semiconductor parts. The carriers move tothe n-type semiconductor part and the p-type semiconductor part underthe influence of the p-n junction. Namely, the electrons move to then-type semiconductor part, and the holes move to the p-typesemiconductor part. Then, the electrons and the holes are collected bythe different electrodes respectively connected to the n-typesemiconductor part and the p-type semiconductor part. The electrodes areconnected to each other using electric wires to thereby obtain electricpower.

SUMMARY OF THE INVENTION

In one aspect, there is a solar cell including a substrate of a firstconductive type, an emitter region of a second conductive type oppositethe first conductive type and which forms a p-n junction along with thesubstrate, an anti-reflection layer positioned on the emitter region, afront electrode part electrically connected to the emitter region, and aback electrode part electrically connected to the substrate, wherein thesubstrate includes a first area formed of single crystal silicon and asecond area formed of polycrystalline silicon, and wherein a thicknessof the anti-reflection layer positioned in the first area is less than athickness of the anti-reflection layer positioned in the second area.

The thickness of the anti-reflection layer positioned in the first areamay be about 60% to 80% of the thickness of the anti-reflection layerpositioned in the second area.

An incident surface of the substrate in the first area may includes aplurality of uneven portions each having a pyramid shape, and anincident surface of the substrate in the second area may not include anuneven portion having a pyramid shape. A distance between upper vertexesof the plurality of uneven portions of the pyramid shape in the firstarea of the substrate may be equal to or less than about 3 μm, and aheight of each of the plurality of uneven portions of the pyramid shapemay be equal to or less than about 4 μm.

An incident surface of the emitter region in the first area of thesubstrate may include a plurality of uneven portions each having apyramid shape, and an incident surface of the emitter region in thesecond area of the substrate may not include an uneven portion having apyramid shape. A thickness of the emitter region in the first area ofthe substrate may be substantially equal to a thickness of the emitterregion in the second area of the substrate.

An incident surface of the anti-reflection layer in the first area ofthe substrate may include a plurality of uneven portions each having apyramid shape, and an incident surface of the anti-reflection layer inthe second area of the substrate may not include an uneven portionhaving a pyramid shape.

The anti-reflection layer may include a first anti-reflection layer,which is positioned directly on the emitter region, and a secondanti-reflection layer, which is positioned directly on the firstanti-reflection layer.

The anti-reflection layer in the first area may have a thickness ofabout 70 nm to 110 nm, and the anti-reflection layer in the second areamay have a thickness of about 100 nm to 140 nm.

A thickness of the first anti-reflection layer in the first area may beabout 30 nm to 50 nm, and a thickness of the second anti-reflectionlayer in the first area may be about 40 nm to 60 nm and is greater thanthe thickness of the first anti-reflection layer in the first area. Athickness of the first anti-reflection layer in the second area may beabout 40 nm to 60 nm, and a thickness of the second anti-reflectionlayer in the second area may be about 60 nm to 80 nm.

A refractive index of the first anti-reflection layer in the first areamay be substantially equal to a refractive index of the firstanti-reflection layer in the second area, and a refractive index of thesecond anti-reflection layer in the first area may be substantiallyequal to a refractive index of the second anti-reflection layer in thesecond area.

The refractive index of the first anti-reflection layer may be greaterthan the refractive index of the second anti-reflection layer. Forexample, the refractive index of the first anti-reflection layer may beabout 2.1 to 2.3, and the refractive index of the second anti-reflectionlayer may be about 1.75 to 1.9.

The anti-reflection layer may be formed of silicon nitride.

The first anti-reflection layer and the second anti-reflection layer maybe formed of silicon nitride.

The second area of the substrate may be flatter than the first area ofthe substrate.

An incident surface of the emitter region positioned in the second areaof the substrate may be flatter than an incident surface of the emitterregion positioned in the first area of the substrate. An incidentsurface of the anti-reflection layer positioned in the second area ofthe substrate may be flatter than an incident surface of theanti-reflection layer positioned in the first area of the substrate.

The front electrode part may be formed on the first area and the secondarea.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a partial perspective view of a solar cell according to anexample embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1;

FIG. 3 illustrates in detail a substrate of the solar cell shown inFIGS. 1 and 2;

FIG. 4 is an enlarged view of a portion ‘A’ corresponding to a firstarea and a portion ‘B’ corresponding to a second area shown in FIG. 2;and

FIG. 5 illustrates a reflectance of an anti-reflection layer dependingon a wavelength of light.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the invention,examples of which are illustrated in the accompanying drawings. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts. It should be noted thata detailed description of known arts will be omitted if the known artscan obscure the embodiments of the invention.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. It will be understood that when an elementsuch as a layer, film, region, or substrate is referred to as being “on”another element, it can be directly on the other element or interveningelements may also be present. In contrast, when an element is referredto as being “directly on” another element, there are no interveningelements present. Further, it will be understood that when an elementsuch as a layer, film, region, or substrate is referred to as being“entirely” on other element, it may be on the entire surface of theother element and may be not on a portion of an edge of the otherelement.

Example embodiments of the invention will be described with reference toFIGS. 1 to 5.

A solar cell according to an example embodiment of the invention isdescribed in detail with reference to FIGS. 1 and 2.

FIG. 1 is a partial perspective view of a solar cell according to anexample embodiment of the invention, and FIG. 2 is a cross-sectionalview taken along line II-II of FIG. 1.

As shown in FIGS. 1 and 2, a solar cell 1 according to an exampleembodiment of the invention may include a substrate 110, an emitterregion 120 positioned at a front surface of the substrate 110 on whichlight is incident, an anti-reflection layer 130 positioned on theemitter region 120, a back surface field region 170 positioned at a backsurface of the substrate 110, a front electrode part 150 positioned onthe emitter region 120, and a back electrode part 160 positioned on theback surface of the substrate 110. In another embodiment, the backsurface field region 170 may be omitted, if necessary or desired.

The substrate 110 may contain impurities of a first conductive type, forexample, p-type impurities.

When the substrate 110 is of a p-type, the substrate 110 may containimpurities of a group III element such as boron (B), gallium (Ga), andindium (In). Alternatively, the substrate 110 may be of an n-type and/ormay be formed of a semiconductor material other than silicon. When thesubstrate 110 is of the n-type, the substrate 110 may contain impuritiesof a group V element such as phosphorus (P), arsenic (As), and antimony(Sb).

When light irradiated onto the solar cell 1 is incident on the substrate110, electron-hole pairs are produced by light energy based on theincident light.

The substrate 110 includes a first area (or a first portion) S1 formedof single crystal silicon and a second area (or a second portion) S2formed of polycrystalline silicon. When a texturing process is performedon the incident surface (i.e., the front surface) of the substrate 110,crystal orientations of the first area S1 (i.e., the single crystalsilicon area) are uniform, and thus a plurality of uneven portions eachhaving a pyramid shape are formed in the first area S1. On the otherhand, crystal orientations of the second area S2 (i.e., thepolycrystalline silicon area) are not uniform, and thus, a plurality ofuneven portions having not a uniform pattern (for example, a pyramidshape) but a non-uniform pattern are formed in the second area S2.Heights of the uneven portions in the second area S2 are much less thanheights of the uneven portions in the first area S1. Thus, the secondarea S2 has an almost flat surface, as compared to the first area S1.This will be described in detail later with reference to FIG. 3.

The emitter region 120 is entirely formed at the front surface (or theincident surface) of the substrate 110. The emitter region 120 is aregion doped with impurities of a second conductive type (for example,the n-type) opposite the first conductive type of the substrate 110.Thus, the emitter region 120 of the second conductive type forms a p-njunction along with a first conductive type region of the substrate 110.

The electrons and the holes produced by light incident on the substrate110 respectively move to the n-type semiconductor and the p-typesemiconductor by a built-in potential difference resulting from the p-njunction between the substrate 110 and the emitter region 120. Thus,when the substrate 110 is of the p-type and the emitter region 120 is ofthe n-type, the holes move to the substrate 110 and the electrons moveto the emitter region 120.

Because the emitter region 120 forms the p-n junction along with thesubstrate 110, the emitter region 120 may be of the p-type if thesubstrate 110 is of the n-type in another embodiment. In this instance,the holes may move to the emitter region 120, and the electrons may moveto the substrate 110.

When the emitter region 120 is of the n-type, the emitter region 120 maybe formed by doping the substrate 110 with impurities of a group Velement such as phosphorus (P), arsenic (As), and antimony (Sb).Alternatively, when the emitter region 120 is of the p-type, the emitterregion 120 may be formed by doping the substrate 110 with impurities ofa group III element such as boron (B), gallium (Ga), and indium (In).

As shown in FIGS. 1 and 2, an incident surface of the emitter region 120positioned in the first area S1 has a plurality of uneven portions eachhaving a pyramid shape in conformity with the shapes of the plurality ofuneven portions formed on the incident surface of the substrate 110 inthe first area S1. Further, an incident surface of the emitter region120 positioned in the second area S2 does not have uneven portionshaving the pyramid shape in conformity with the shape of the incidentsurface of the substrate 110 in the second area S2. Thus, the incidentsurface of the emitter region 120 in the second area S2 is flatter ormore even than the incident surface of the emitter region 120 in thefirst area S1.

The anti-reflection layer 130 prevents light incident from the outsidefrom being again reflected to the outside. The anti-reflection layer 130is formed on a front surface of the emitter region 120. Morespecifically, the anti-reflection layer 130 may be formed on the frontsurface of the emitter region 120, on which the front electrode part 150is not formed.

The anti-reflection layer 130 may be formed of a transparent material,for example, hydrogenated silicon nitride (SiNx:H), hydrogenated siliconoxide (SiOx:H), or hydrogenated silicon oxynitride (SiOxNy:H).

The anti-reflection layer 130 reduces a reflectance of light incident onthe solar cell 1 and increases selectivity of a predetermined wavelengthband, thereby increasing the efficiency of the solar cell 1.

The anti-reflection layer 130 performs a passivation function whichconverts a defect, for example, dangling bonds existing at and aroundthe surface of the emitter region 120 into stable bonds using hydrogen(H) used to form the anti-reflection layer 130 to thereby prevent orreduce a recombination and/or a disappearance of carriers moving to thesurface of the emitter region 120. Hence, the efficiency of the solarcell 1 is improved.

As shown in FIGS. 1 and 2, an incident surface of the anti-reflectionlayer 130 positioned in the first area S1 has a plurality of unevenportions each having a pyramid shape in conformity with the shapes ofthe plurality of uneven portions formed on the incident surface of thesubstrate 110 in the first area S1. Further, an incident surface of theanti-reflection layer 130 positioned in the second area S2 does not haveuneven portions having the pyramid shape in conformity with the shape ofthe incident surface of the substrate 110 in the second area S2. Thus,the incident surface of the anti-reflection layer 130 in the second areaS2 is flatter or more even than the incident surface of theanti-reflection layer 130 in the first area S1.

A thickness of the anti-reflection layer 130 in the first area S1 of thesubstrate 110 may be different from a thickness of the anti-reflectionlayer 130 in the second area S2 of the substrate 110 because of adifference between surface areas of the incident surface of thesubstrate 110 per a unit surface area of the substrate 110. Namely, thethickness of the anti-reflection layer 130 in the first area S1 may beless than the thickness of the anti-reflection layer 130 in the secondarea S2. This will be described in detail later with reference to FIG.4.

In the embodiment of the invention, the anti-reflection layer 130 has amulti-layered structure, including for example, a double-layeredstructure. Alternatively, the anti-reflection layer 130 may have asingle-layered structure.

In the embodiment of the invention, the anti-reflection layer 130 has adouble-layered structure including a first anti-reflection layer 131 anda second anti-reflection layer 132. The first anti-reflection layer 131abuts on the emitter region 120 and is positioned directly on theemitter region 120. The second anti-reflection layer 132 abuts on thefirst anti-reflection layer 131 and is positioned directly on the firstanti-reflection layer 131.

A refractive index of the first anti-reflection layer 131 may be greaterthan a refractive index of the second anti-reflection layer 132. Forexample, the refractive index of the first anti-reflection layer 131 maybe about 2.1 to 2.3, and the refractive index of the secondanti-reflection layer 132 may be about 1.75 to 1.9.

The first anti-reflection layer 131 may be formed of silicon nitride(SiNx), for example. The first anti-reflection layer 131 performs thepassivation function that converts a defect, for example, dangling bondsexisting at and around the surface of the emitter region 120 into stablebonds to thereby prevent or reduce a recombination and/or adisappearance of carriers moving to the emitter region 120. Further, thefirst anti-reflection layer 131 reduces a reflectance of light incidenton the substrate 110. The first anti-reflection layer 131 has therefractive index of about 2.1 to 2.3.

When the refractive index of the first anti-reflection layer 131 is lessthan about 2.1, an anti-reflection operation of the firstanti-reflection layer 131 is not well performed because of a smoothreflection of light. Hence, the passivation effect of the firstanti-reflection layer 131 is reduced, and the efficiency of the solarcell 1 is reduced. When the refractive index of the firstanti-reflection layer 131 is greater than about 2.3, the photoelectricefficiency of the substrate 110 is reduced because light incident on thesubstrate 110 is absorbed in the first anti-reflection layer 131.

The second anti-reflection layer 132 is positioned only on the firstanti-reflection layer 131. The second anti-reflection layer 132 may beformed of silicon nitride (SiNx) in the same manner as the firstanti-reflection layer 131. The second anti-reflection layer 132 has therefractive index of about 1.75 to 1.9.

The first and second anti-reflection layers 131 and 132 reduce areflectance of light incident on the substrate 110 and increase anamount of light absorbed in the substrate 110. Further, the secondanti-reflection layer 132 further improves the passivation effect due tohydrogen (H) contained in silicon nitride (SiNx).

As described above, the refractive index of the second anti-reflectionlayer 132 is less than the refractive index of the first anti-reflectionlayer 131. Therefore, the anti-reflection effect of the secondanti-reflection layer 132 may be better than the first anti-reflectionlayer 131, but the passivation effect of the second anti-reflectionlayer 132 may be poorer than the first anti-reflection layer 131.

When the refractive index of the second anti-reflection layer 132 isless than about 1.75, an anti-reflection operation of the secondanti-reflection layer 132 is not well performed because of a smoothreflection of light. When the refractive index of the secondanti-reflection layer 132 is greater than about 1.9, the photoelectricefficiency of the substrate 110 is reduced because light incident on thesubstrate 110 is absorbed in the second anti-reflection layer 132.

As shown in FIG. 1, the front electrode part 150 includes a plurality offinger electrodes 151 and a plurality of front bus bars 152 crossing thefinger electrodes 151. The front electrode part 150 is formed on thefront surface of the emitter region 120 and is electrically connected tothe emitter region 120. Alternatively, the plurality of front bus bars152 may be omitted in another embodiment.

The finger electrodes 151 and the front bus bars 152 are connected toeach other. The finger electrodes 151 are separated from one another andextend parallel to one another in a fixed direction. Further, the frontbus bars 152 are separated from one another and extend parallel to oneanother in a fixed direction. The finger electrodes 151 and the frontbus bars 152 collect carriers (for example, electrons) moving to theemitter region 120.

The front bus bars 152 are positioned on the same level layer as thefinger electrodes 151 and are electrically and physically connected tothe finger electrodes 151 at crossings of the finger electrodes 151 andthe front bus bars 152.

As shown in FIG. 1, the plurality of finger electrodes 151 may bedisposed in a stripe shape extending in a transverse or longitudinaldirection, and the plurality of front bus bars 152 may be disposed in astripe shape extending in a longitudinal or transverse direction. Thus,the front electrode part 150 may have a lattice shape on the frontsurface of the substrate 110.

The front bus bars 152 collect not only carriers (for example,electrons) moving from the emitter region 120 but also carrierscollected by the finger electrodes 151 crossing the front bus bars 152,and move the collected carriers in a desired direction. Thus, a width ofeach front bus bar 152 may be greater than a width of each fingerelectrode 151.

The front bus bars 152 are connected to an external device and outputthe collected carriers to the external device. The front electrode part150 including the finger electrodes 151 and the front bus bars 152 isformed of at least one conductive material such as silver (Ag).

In the embodiment of the invention, the number of finger electrodes 151and the number of front bus bars 152 may vary, if necessary or desired.In embodiments of the invention, the front electrode part 150 includingthe plurality of finger electrodes 151 and/or a plurality of front busbars 152 may be formed at least on the first area S1 and the second areaS2. For example, the front electrode part 150 may be formed on both thefirst area S1 and the second area S2.

The back surface field region 170 is a region (for example, a p⁺-typeregion) that is more heavily doped than the substrate 110 withimpurities of the same conductive type as the substrate 110.

A potential barrier is formed by a difference between impurityconcentrations of the first conductive type region (for example, ap-type region) of the substrate 110 and the back surface field region170. Hence, the potential barrier prevents or reduces electrons frommoving to the back surface field region 170 used as a moving path ofholes and makes it easier for the holes to move to the back surfacefield region 170. Thus, the back surface field region 170 reduces anamount of carriers lost by a recombination and/or a disappearance ofelectrons and holes at and around the back surface of the substrate 110and accelerate a movement of desired carriers (for example, holes),thereby increasing an amount of carriers moving to the back electrodepart 160.

As shown in FIG. 1, the back electrode part 160 positioned on the backsurface of the substrate 110 includes a back electrode 161 and aplurality of back bus bars 162. In another embodiment, the back bus bars162 may be omitted, if necessary or desired.

The back electrode 161 contacts the back surface field region 170positioned at the back surface of the substrate 110 and is positioned onthe entire back surface of the substrate 110 except a formation area ofthe back bus bars 162. In another embodiment, the back electrode 161 maybe not positioned at an edge of the back surface of the substrate 110.The back electrode 161 is formed of at least one conductive materialsuch as aluminum (Al).

The back electrode 161 collects carriers (for example, holes) moving tothe back surface field region 170.

Because the back electrode 161 contacts the back surface field region170 having the impurity concentration higher than the substrate 110, acontact resistance between the substrate 110 (i.e., the back surfacefield region 170) and the back electrode 161 is reduced. Hence, thetransfer efficiency of carriers from the substrate 110 to the backelectrode 161 is improved.

The back bus bars 162 are positioned on the back surface of thesubstrate 110, on which the back electrode 161 is not positioned, andare connected to the back electrode 161. The back bus bars 162 and theback electrode 161 are positioned on the same level layer on the backsurface of the substrate 110.

The back bus bars 162 collect carriers transferred from the backelectrode 161 in the same manner as the front bus bars 152.

The back bus bars 162 are connected to the external device, and carriers(for example, holes) collected by the back bus bars 162 are output tothe external device.

The back bus bars 162 may be formed of a material having betterconductivity than the back electrode 161. For example, the back bus bars162 may contain at least one conductive material such as silver (Ag),unlike the back electrode 161.

The back bus bars 162 extend parallel to one another in the samedirection as an extension direction of the front bus bars 152 and areseparated from one another. The back bus bars 162 are positionedopposite the front bus bars 152 with the substrate 110 interposedtherebetween. In the embodiment of the invention, the number of back busbars 162 may be equal to the number of front bus bars 152, and may bealigned.

For example, the back bus bars 162 may have a stripe shape in adirection parallel to the front bus bars 152.

An operation of the solar cell 1 having the above-described structure isdescribed below.

When light irradiated to the solar cell 11 is incident on the emitterregion 120 and the substrate 110, each of which is the semiconductorpart, through the anti-reflection layer 130, electrons and holes aregenerated in the emitter region 120 and the substrate 110 by lightenergy produced based on the incident light. In this instance, because areflection loss of the light incident on the substrate 110 is reduced bythe anti-reflection layer 130, an amount of light incident on thesubstrate 110 increases.

The electrons move to the n-type emitter region 120 and the holes moveto the p-type substrate 110 by the p-n junction of the substrate 110 andthe emitter region 120.

The electrons moving to the emitter region 120 are collected by thefinger electrodes 151 and the front bus bars 152, and then move alongthe front bus bars 152. The holes moving to the substrate 110 arecollected by the back electrode 161 and the back bus bars 162, and thenmove along the back bus bars 162. When the front bus bars 152 areconnected to the back bus bars 162 using electric wires, current flowstherein to thereby enable use of the current for electric power.

FIG. 3 illustrates in detail a substrate of the solar cell shown inFIGS. 1 and 2.

In FIG. 3, (a) illustrates the incident surface of the substrate 110after the texturing process is performed; (b) is an enlarged view of thefirst area S1 (i.e., the single crystal silicon area) in the incidentsurface of the substrate 110; and (c) is an enlarged view of the secondarea S2 (i.e., the polycrystalline silicon area) in the incident surfaceof the substrate 110.

As shown in (a) of FIG. 3, the substrate 110 according to the embodimentof the invention includes the first area S1 (i.e., the single crystalsilicon area) and the second area S2 (i.e., the polycrystalline siliconarea).

More specifically, as shown in (a) of FIG. 3, formation positions andformation sizes of the first area S1 and the second area S2 in thesubstrate 110 may be randomly determined without a specific pattern andrule.

As shown in (b) of FIG. 3, when the texturing process is performed onthe incident surface of the substrate 110, the first area S1 of thesubstrate 110 may have a plurality of uneven portions each having apyramid shape.

A distance PD between upper vertexes of the uneven portions P having thepyramid shape formed in the first area S1 of the substrate 110 may beequal to or less than about 3 μm. A height PH of each uneven portion Pmay be equal to or less than about 4 μm.

As shown in (c) of FIG. 3, after the texturing process was performed onthe incident surface of the substrate 110, in the second area S2, aplurality of relatively almost flat uneven portions having a non-uniformand random pattern may be formed, a plurality of uneven portions havinga uniform pattern (for example, a pyramid shape) may be not formed inthe second area S2. Because the crystal orientations of the second areaS2 of the substrate 110 are not uniform because of the properties ofpolycrystalline silicon. Even if the uneven portions are formed in thesecond area S2, heights of the uneven portions in the second area S2 maybe much less than the heights of the uneven portions in the first areaS1. Thus, the second area S2 may have the relatively almost flat surfacehaving the non-uniform shape, as compared to the first area S1.

The surface area of the first area S1 is greater than the surface areaof the second area S2 based on a unit area, for example, 1 μm² of thesubstrate 110 including the first and second areas S1 and S2.

The substrate 110 including the first area S1 (i.e., the single crystalsilicon area) and the second area S2 (i.e., the polycrystalline siliconarea) has better characteristics than a substrate formed only ofpolycrystalline silicon. Namely, the substrate 110 has a bulk lifetimeof carriers longer than the polycrystalline silicon substrate and ischeaper than the polycrystalline silicon substrate.

The solar cell 1 according to the embodiment of the invention may usemore carriers generated inside the substrate 110 than around the surfaceof the substrate 110 through the substrate 110 having theabove-described structure.

In other words, because the solar cell 1 according to the embodiment ofthe invention may use carriers generated inside the substrate 110, thesubstrate 110 may further increase an amount of current generated in thesolar cell 1 than a solar cell of only the polycrystalline siliconsubstrate. Hence, the efficiency of the solar cell 1 may be improved.

As described above, because the solar cell 1 according to the embodimentof the invention includes the substrate 110 including the first andsecond areas S1 and S2, the thickness of the anti-reflection layer 130positioned on the front surface of the substrate 110 may vary. This isdescribed in detail with reference to FIG. 4.

FIG. 4 is an enlarged view of a portion ‘A’ corresponding to the firstarea S1 and a portion ‘B’ corresponding to the second area S2 shown inFIG. 2. In particular, (a) of FIG. 4 is an enlarged view of the portion‘A’ corresponding to the first area S1, and (b) of FIG. 4 is an enlargedview of the portion ‘B’ corresponding to the second area S2.

As shown in (a) and (b) of FIG. 4, the emitter region 120 and theanti-reflection layer 130 are formed on the first area S1 having theuneven portions of the pyramid shape and the second area S2 not havingthe uneven portions of the pyramid shape.

In this instance, because the second conductive type impurities of theemitter region 120 are diffused and doped into the substrate 110, athickness ET1 of the emitter region 120 in the first area S1 issubstantially equal to a thickness ET1 of the emitter region 120 in thesecond area S2. However, the incident surface of the emitter region 120on the first area S1 has a plurality of uneven portions each having thepyramid shape in conformity with the shapes of the uneven portionsformed on the incident surface of the substrate 110 in the first areaS1. Further, the incident surface of the emitter region 120 on thesecond area S2 does not have uneven portions of the pyramid shape inconformity with the shape of the incident surface of the substrate 110in the second area S2. Thus, the incident surface of the emitter region120 in the second area S2 is flatter or more even than the incidentsurface of the emitter region 120 in the first area S1.

As a result, the surface area of the emitter region 120 in the firstarea S1 is greater than the surface area of the emitter region 120 inthe second area S2 based on the unit area of the substrate 110.

The formation material of the anti-reflection layer 130 is distributedand stacked on the emitter region 120. In this instance, an amount offormation material of the anti-reflection layer 130 distributed on theemitter region 120 in the first area S1 is substantially equal to anamount of formation material of the anti-reflection layer 130distributed on the emitter region 120 in the second area S2 based on theunit area of the substrate 110.

However, a thickness of the anti-reflection layer 130 formed in thefirst area S1 of the substrate 110 is less than a thickness of theanti-reflection layer 130 formed in the second area S2 of the substrate110 because of a difference between the surface areas of the first areaS1 and the second area S2.

In this instance, if the total thickness of the anti-reflection layer130 is determined based on the first area S1, the anti-reflection layer130 formed in the second area S2 may be excessively thick because of adifference between the thicknesses of the anti-reflection layer 130formed in the first area S1 and the second area S2. Further, if thetotal thickness of the anti-reflection layer 130 is determined based onthe second area S2, the anti-reflection layer 130 formed in the firstarea S1 may be excessively thin because of the difference between thethicknesses of the anti-reflection layer 130 formed in the first area S1and the second area S2.

Hence, an optical loss may be generated or the passivation effect may bereduced. As a result, the photoelectric conversion efficiency of thesolar cell 1 may be better than that of the solar cell including thepolycrystalline silicon substrate.

However, as described above with reference to FIG. 3, if light of a longwavelength band capable of generating more carriers inside the substrate110 than around the surface of the substrate 110 is used inconsideration of the relatively long bulk lifetime of carriers, thephotoelectric conversion efficiency of the solar cell 1 may be furtherimproved.

The refractive index of the first anti-reflection layer 131 may be setto about 2.1 to 2.3 and the refractive index of the secondanti-reflection layer 132 may be set to about 1.75 to 1.9, so as to moreefficiently use light of the long wavelength band. In this instance, arefractive index of the anti-reflection layer 130 in the first area S1and a refractive index of the anti-reflection layer 130 in the secondarea S2 are set to be substantially equal to each other.

The entire thickness of the anti-reflection layer 130 in the first areaS1 may be about 70 nm to 110 nm, and the entire thickness of theanti-reflection layer 130 in the second area S2 may be about 100 nm to140 nm.

The entire thickness of the anti-reflection layer 130 in the first areaS1 may be about 60% to 80% of the entire thickness of theanti-reflection layer 130 in the second area S2 within the abovethickness range of the anti-reflection layer 130.

More specifically, a thickness ARTa1 of the first anti-reflection layer131 in the first area S1 may be about 30 nm to 50 nm, and a thicknessARTa2 of the second anti-reflection layer 132 in the first area S1 maybe about 40 nm to 60 nm and may be greater than the thickness ARTa1 ofthe first anti-reflection layer 131 in the first area S1.

Further, a thickness ARTb1 of the first anti-reflection layer 131 in thesecond area S2 may be about 40 nm to 60 nm, and a thickness ARTb2 of thesecond anti-reflection layer 132 in the second area S2 may be about 60nm to 80 nm and may be greater than the thickness ARTb1 of the firstanti-reflection layer 131 in the second area S2.

The solar cell 1 according to the embodiment of the invention sets therefractive indexes and the thicknesses of the first anti-reflectionlayer 131 and the second anti-reflection layer 132 to theabove-described values, thereby reducing a reflectance of light of thelong wavelength band of about 700 nm to 1,000 nm and further increasingthe photoelectric conversion efficiency of the solar cell 1.

FIG. 5 illustrates a reflectance of the anti-reflection layer dependingon a wavelength of light.

In FIG. 5, (a) illustrates a reflectance depending on a wavelength oflight in the first area S1 of the substrate 110, and (b) illustrates areflectance depending on a wavelength of light in the second area S2 ofthe substrate 110.

In (a) and (b) of FIG. 5, ‘case1’ indicates an example of using thefirst anti-reflection layer 131 as the anti-reflection layer, and‘case2’ indicates an example of using the first and secondanti-reflection layers 131 and 132 as the anti-reflection layer.

In (a) and (b) of FIG. 5, the easel used the first anti-reflection layer131 which has a single-layered structure and a refractive index of about2.2.

A thickness of the first anti-reflection layer 131 in the first area S1was set to about 35 nm, and a thickness of the first anti-reflectionlayer 131 in the second area S2 was set to about 50 nm.

Further, in (a) and (b) of FIG. 5, the case2 used the anti-reflectionlayer having a double-layered structure. More specifically, a refractiveindex and a thickness of the first anti-reflection layer 131 used as alower layer were substantially equal to those of the firstanti-reflection layer 131 used in the case1. A refractive index of thesecond anti-reflection layer 132 positioned on the first anti-reflectionlayer 131 was set to about 1.8. Further, a thickness of the secondanti-reflection layer 132 in the first area S1 was set to about 50.5 nm,and a thickness of the second anti-reflection layer 132 in the secondarea S2 was set to about 72 nm.

In (a) and (b) of FIG. 5, the refractive indexes and the thicknesses ofthe single-layered anti-reflection layer of the case1 and thedouble-layered anti-reflection layer of the case2 were set within therange of the anti-reflection layer 130 according to the embodiment ofthe invention, so as to increase an absorptance of light of the longwavelength band.

As shown in (a) and (b) of FIG. 5, a reflectance of light of the longwavelength band of about 700 nm to 1,000 nm was equal to or less thanabout 10% and was good.

Further, a reflectance of the double-layered anti-reflection layer ofthe case2 was less than a reflectance of the single-layeredanti-reflection layer of the case1 in a middle wavelength band less thanabout 700 nm and a short wavelength band, and thus an absorptance of thedouble-layered anti-reflection layer of the case2 was further improved.

More specifically, as shown in (a) of FIG. 5, a reflectance of thedouble-layered anti-reflection layer in the first area S1 of thesubstrate 110 was much less than a reflectance of the single-layeredanti-reflection layer in the first area S1 of the substrate 110 in theshort wavelength band equal to or less than about 450 nm. Further, asshown in (b) of FIG. 5, a reflectance of the double-layeredanti-reflection layer in the second area S2 of the substrate 110 wasmuch less than a reflectance of the single-layered anti-reflection layerin the second area S2 of the substrate 110 in the middle wavelength bandof about 550 nm and the short wavelength band.

As described above, the photoelectric efficiency of the solar cellaccording to the embodiment of the invention is improved using thesubstrate including the first area formed of single crystal silicon andthe second area formed of polycrystalline silicon, and also themanufacturing cost of the solar cell is greatly reduced. Furthermore,the refractive index and the thickness of the anti-reflection layer areset in consideration of the bulk lifetime of carriers, so as to increasethe absorptance of light of the long wavelength band, and thus thephotoelectric conversion efficiency of the solar cell is furtherimproved.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the scope of the principles of thisdisclosure. More particularly, various variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A solar cell comprising: a substrate of a firstconductive type; an emitter region of a second conductive type oppositethe first conductive type and which forms a p-n junction along with thesubstrate; an anti-reflection layer positioned on the emitter region; afront electrode part electrically connected to the emitter region; and aback electrode part electrically connected to the substrate, wherein thesubstrate includes a first area formed of single crystal silicon and asecond area formed of polycrystalline silicon, wherein a thickness ofthe anti-reflection layer positioned on the first area is less than athickness of the anti-reflection layer positioned on the second area,wherein a roughness of an incident surface of the substrate in the firstarea is different from a roughness of the incident surface of thesubstrate in the second area, and wherein the emitter region is entirelyformed on the incident surface of the substrate.
 2. The solar cell ofclaim 1, wherein the thickness of the anti-reflection layer positionedon the first area is 60% to 80% of the thickness of the anti-reflectionlayer positioned in the second area.
 3. The solar cell of claim 1,wherein the incident surface of the substrate in the first area includesa plurality of uneven portions each having a pyramid shape, and theincident surface of the substrate in the second area does not include anuneven portion having a pyramid shape.
 4. The solar cell of claim 3,wherein a distance between upper vertexes of the plurality of unevenportions of the pyramid shape in the first area of the substrate isequal to or less than 3 μm, and a height of each of the plurality ofuneven portions of the pyramid shape is equal to or less than 4 μm. 5.The solar cell of claim 1, wherein an incident surface of the emitterregion on the first area of the substrate includes a plurality of unevenportions each having a pyramid shape, and an incident surface of theemitter region on the second area of the substrate does not include anuneven portion having a pyramid shape.
 6. The solar cell of claim 5,wherein a thickness of the emitter region on the first area of thesubstrate is substantially equal to a thickness of the emitter region onthe second area of the substrate.
 7. The solar cell of claim 1, whereinan incident surface of the anti-reflection layer on the first area ofthe substrate includes a plurality of uneven portions each having apyramid shape, and an incident surface of the anti-reflection layer onthe second area of the substrate does not include an uneven portionhaving a pyramid shape.
 8. The solar cell of claim 1, wherein theanti-reflection layer on the first area has a thickness of 70 nm to 110nm, and the anti-reflection layer on the second area has a thickness of100 nm to 140 nm.
 9. The solar cell of claim 1, wherein theanti-reflection layer includes a first anti-reflection layer, which ispositioned on the emitter region, and a second anti-reflection layer,which is positioned on the first anti-reflection layer.
 10. The solarcell of claim 9, wherein a thickness of the first anti-reflection layeron the first area is 30 nm to 50 nm, and a thickness of the secondanti-reflection layer on the first area is 40 nm to 60 nm and is greaterthan the thickness of the first anti-reflection layer on the first area.11. The solar cell of claim 9, wherein a thickness of the firstanti-reflection layer on the second area is 40 nm to 60 nm, and athickness of the second anti-reflection layer on the second area is 60nm to 80 nm.
 12. The solar cell of claim 9, wherein a refractive indexof the first anti-reflection layer on the first area is substantiallyequal to a refractive index of the first anti-reflection layer in thesecond area, and a refractive index of the second anti-reflection layeron the first area is substantially equal to a refractive index of thesecond anti-reflection layer on the second area.
 13. The solar cell ofclaim 12, wherein the refractive index of the first anti-reflectionlayer is greater than the refractive index of the second anti-reflectionlayer.
 14. The solar cell of claim 13, wherein the refractive index ofthe first anti-reflection layer is 2.1 to 2.3, and the refractive indexof the second anti-reflection layer is 1.75 to 1.9.
 15. The solar cellof claim 9, wherein the first anti-reflection layer and the secondanti-reflection layer are formed of silicon nitride.
 16. The solar cellof claim 1, wherein the anti-reflection layer is formed of siliconnitride.
 17. The solar cell of claim 1, wherein an overall surfaceroughness of the second area of the substrate is flatter than an overallsurface roughness of the first area of the substrate.
 18. The solar cellof claim 1, wherein an overall surface roughness of the emitter regionpositioned on the second area of the substrate is flatter than anoverall surface roughness of the emitter region positioned on the firstarea of the substrate.
 19. The solar cell of claim 1, wherein an overallsurface roughness of the anti-reflection layer positioned on the secondarea of the substrate is flatter than an overall surface roughness ofthe anti-reflection layer positioned on the first area of the substrate.20. The solar cell of claim 1, wherein the front electrode part isformed on the first area and the second area.